The present invention relates to security documents such as banknotes or the like, and is particularly concerned with providing a security document which includes a magnetic device or watermark for verifying the authenticity of the security document. The invention is also concerned with a method of producing such security documents.
A wide variety of security devices or features for security documents, such as banknotes, travellers cheques or the like have been previously proposed. One such security device is a xe2x80x9cmagnetic watermarkxe2x80x9d in which a coating of selectively oriented magnetic particles in a binder is applied to a security document. The magnetic watermark is formed by applying a magnetic field to preselected areas of the coating whilst it is in a liquid state, and then causing the coating to solidify.
U.S. Pat. No. 4,186,944 describes one method of applying such a security device to a paper banknote. According to this method, magnetic particles are firstly mixed with the ink which will be used to apply indicia to the surface of the banknote. After mixing, the ink is poured into a cell, then heated, and placed in a magnetic field to orient the magnetic particles in the cell in a particular pattern or design. The banknote is next brought into contact with the cell so that the wet ink is transferred onto one of its surfaces. The transferred ink is absorbed through the surface of the paper and allowed to cool, which causes the orientation of magnetic particles in the transferred ink to be maintained.
A disadvantage of this method is that, in addition to being complex, it requires the magnetic watermark to be coincident with the printed indicia on the security document, rather than being hidden from visual inspection elsewhere on the document. Moreover, such a method is particularly unsuitable for use in polymer based banknotes, which are formed at least in part from plastics materials, and like security documents. Such documents comprise a flexible film substrate which is coated on one or both sides with an opacifying pigmentary layer. The substrate is then passed through a printing machine to print indicia onto one or both of the opacifying layers. Heating of the ink used to print the relevant indicia on the banknote, so as to allow the orientation of magnetic particles therewithin, could produce a disturbance in the opacifying layer and/or the substrate.
It is therefore desirable to provide a security document and method of producing such security document which allows the convenient application of a magnetic watermark.
It is also desirable to provide a security document and method of producing such security document which enables the orientation of magnetic particles constituting the watermark to be carried out without undue disturbance to the security document itself.
It is further desirable to provide a security document and method of producing such security document which ameliorates or overcomes one or more problems associated with the prior art.
One aspect of the present invention provides a method of producing a security document, comprising the steps of:
(a) forming a sheet-like substrate of plastics material having first and second opposing surfaces,
(b) coating a first layer of polymer material containing magnetic particles on said first opposing surface,
(c) melting at least a portion of said first layer such that the magnetic particles can orient under the influence of a magnetic field,
(d) applying said magnetic field so as to form a magnetic watermark, and
(e) allowing said first layer portion to cool so as to fix the orientation of said magnetic particles.
Preferably, the first layer is at least partially transparent.
The first layer may act to protect the security document from wear.
The first layer may include particles acting to improve the adherence of the security document when handled by a user.
The sheet-like substrate preferably comprises a film having first and second opposing sides, and the method may further comprise the step of coating at least one of said first or second opposing sides with an opacifying coating prior to step (c).
The method preferably further comprises the step of forming indicia on at least said first opacifying coating after step (a).
The protective layer may be melted in step (d) by the application of induction heating.
Alternatively, the protective layer in step (d) may be melted by subjecting its outer surface to a heated die or roller.
The heated die or roller may have a shape similar or corresponding to said magnetic watermark, and the heated die may be borne on the surface of a rotatably driven roller.
A further aspect of the present invention provides a method of producing a security document, comprising the steps of:
(a) forming a sheet-like substrate of plastics material having first and second opposing surfaces,
(b) coating a first layer of polymer on said first opposing surface,
(c) placing magnetic particles in the adhesive of a transfer foil,
(d) placing the transfer foil on said first layer,
(e) melting at least a portion of said first layer,
(f) pressing said transfer foil so that the magnetic particles are transferred into said melted first layer portion,
(g) applying said magnetic field so as to orient said magnetic particles and thereby form a magnetic watermark, and
(h) allowing said first layer portion to cool so as to fix the orientation of said magnetic particles.
Preferably, the first layer is at least partially transparent.
The first layer may act to protect the security document from wear.
The first layer may include particles acting to improve the adherence of the security document when handled by a user.
The sheet-like substrate may comprise a film having first and second opposing sides, said method further comprising the step of coating at least one of said first or second opposing sides with an opacifying coating prior to step (b).
The method may further comprise the step of forming indicia on at least said first opacifying coating after step (a).
Yet another aspect of the present invention provides a method of producing a security document, comprising the steps of:
(a) forming a sheet-like substrate of plastics material having first and second opposing outer layers containing magnetic particles,
(b) melting at least a portion of one of said outer layers such that the magnetic particles can orient under the influence of a magnetic field,
(c) applying said magnetic field so as to form a magnetic watermark,
(d) allowing said outer layer portion to cool so as to fix the orientation of said magnetic particles, and
(e) coating a protective layer of polymer material on said outer layer.
The protective layer may be at least partially transparent.
The protective layer may act to protect the security document from wear.
The protective layer may include particles acting to improve the adherence of the security document when handled by a user.
The method may further comprise the step of coating an opacifying layer on said first and second outer layers after step (d).
The method may also comprise the step of forming indicia on said opacifying layer.
The protective layer may be melted in step (d) by the application of induction heating.
Alternatively, the protective layer in step (d) may be melted by subjecting its outer surface to a heated die or roller.
The heated die or roller may have a shape similar or corresponding to said magnetic watermark.
The heated die may be borne on the surface of a rotatably driven roller.
A still further aspect of the present invention provides a method of producing a security document, comprising the steps of:
(a) forming a sheet-like substrate of plastics material having first and second opposing outer layers containing magnetic particles,
(b) coating an opacifying layer on said first and second outer layers whilst leaving an un-opacified window area in said opacifying layer,
(c) melting at least a portion of one of said outer layers within said window area such that the magnetic particles can orient under the influence of a magnetic field,
(d) applying said magnetic field so as to form a magnetic watermark, and
(e) allowing said outer layer portion to cool so as to fix the orientation of said magnetic particles.
The protective layer may be at least partially transparent.
The protective layer may act to protect the security document from wear.
The protective layer may include particles acting to improve the adherence of the security document when handled by a user.
The method may further comprise the step of coating an opacifying layer on said first and second outer layers after step (d).
The method may also comprise the step of forming indicia on said opacifying layer.
The protective layer may be melted in step (d) by the application of induction heating.
Alternatively, the protective layer step (d) may be melted by subjecting its outer surface to a heated die or roller.
The heated die or roller may have a shape similar or corresponding to said magnetic watermark.
The heated die may be borne on the surface of a rotatably driven roller.